The present invention relates to a disc drive apparatus capable of recording and reproducing data to and from an optical disc-like storage medium. More particularly, the invention relates to a disc drive apparatus that supports a disc-like storage medium having tracks formed physically and in a manner constituting a wobble each on a signal surface of the disc medium.
Disc storage media include DVDs (Digital Versatile Discs or Digital Video Discs) which come in two types: DVD-ROMs for recording purposes only, and DVD-RAMs developed for use as a repeatedly recordable storage medium that has gained widespread acceptance. To write data to a DVD-RAM requires forming recording pits on the disc surface by use of the so-called phase change recording method.
A track format of the DVD-RAM includes recording tracks to and from which data are recorded and reproduced. The recording tracks are divided circumferentially into units called sectors comprising a recordable field each. The recordable field is headed by a header field that has data recorded in pit rows. The recordable field allows data to be recorded thereto repeatedly by the phase change recording method. That is, the header field and recordable field have data stored therein by different data recording methods involving different amounts of laser emission aimed at the disc surface. The tracks comprising recordable fields subject to recording by the phase change recording method are formed so as to constitute a meander shape called “wobble” each. Information derived from the wobble is used illustratively to permit clock recovery and to ensure address reliability.
Briefly, the header field has four addresses: PID1, PID2, PID3 and PID4 in pit rows each identifying a physical address (physical ID). The pit rows of PID1 and PID2 are dislocated by a ½ track pitch on the radially outer side from a center line of each groove track; the pit rows of PID3 and PID4 are dislodged by a ½ track pitch on the radially inner side from the center line. In other words, on each track, the header field and recordable field are radially dislodged by a ½ track pitch each. The DVD-RAM is typically subject to the so-called land/groove recording method whereby data are recorded both to lands and to grooves on the disc.
The above-described DVD-RAM and other recently developed and popularized disc media such as DVD+RW have track formats different from those of conventional CDs and DVD-ROMs. Under the circumstances, disc drive apparatuses that support DVD-RAMs and have recording functions are being called on to provide recording and reproducing performance of higher reliability through improvements addressing these new track formats.